In the related art, a technique for determining a failure of a selective reduction-type catalyst and a failure of a reducing agent supply device based on an average value and a variation of a NOx purification rate available when the ratio of nitrogen dioxide (NO2) that is contained in NOx flowing into the selective reduction-type catalyst (hereinafter, referred to as a “NO2 ratio”) is within a predetermined range and a reducing agent is supplied to the selective reduction-type catalyst has been proposed as a technique for detecting deterioration of the selective reduction-type catalyst (for example, refer to PTL 1).
PTL 2 discloses a configuration in which a membrane containing a selective reduction-type catalyst is formed on a wall surface of a particulate filter that defines an exhaust gas stream and a membrane where pores, which have a size allowing the passage of NOx and preventing the passage of particulate matter (PM), are formed is disposed on a surface of the membrane. This configuration has the purpose of suppressing the thermal deterioration of an SCR catalyst when the PM collected in the particulate filter is oxidized.
PTL 3 discloses a configuration in which a supplemental agent that supplements a sulfur compound in exhaust gas is disposed in an outer layer of a base material and a selective reduction-type catalyst is disposed in a back layer of the base material in a wall flow-type particulate filter.
In PTL 4, a reaction between PM collected in a particulate filter and in exhaust gas is described.